If you don't need the added functionality that a full-function preamp would provide (tape outputs, balance control, mono switch, etc.), my feeling would be that you don't need one.
If your power amp includes a volume control, it essentially incorporates a preamp function, apart from source switching and those other functions. While the possibility exists that adding an active preamp would produce a subjectively more pleasing sound, that would be, if it occurred, the result of euphonic coloration that was masking problems elsewhere, and that would be better addressed elsewhere.
Regards,
-- Al